Naturally occurring and chemically modified ribonucleosides have interesting bioactive effects. Dietary ribonucleosides are ingested mainly as nucleoproteins and are converted in the course of intestinal digestion to monomeric compounds. Different bioactive effects of dietary ribonucleosides have been described, including the ability to enhance gut growth and maturation and to increase iron absorption. Cytochemical studies with human cells showed that several ribonucleosides can induce apoptosis in human cells, and therefore may be potentially anticancerogenic compounds. Even if suboptimal concentrations of single bioactive nucleo compounds are available from food, the total content of different bioactive ribonucleosides may reach physiologically effective concentrations in vivo where intestinal cells may represent the main target sites of a selective apoptotic activity. Modified ribonucleosides serve as valuable pathobiochemical marker molecules for cancer. Chemically modified ribonucleosides have already found interesting applications as pharmaceutically active compounds in the treatment of different illnesses including AIDS. Regarding therapeutic and pharmaceutical aspects, further studies are required to evaluate the bioactive efficacy of indigenous ribonucleosides. The findings demonstrate the great variety of potential applications of ribonucleosides, e.g. in functional foods as well as pharmaceutical preparations.